CI1.5 利用字符重复的次数压缩字符

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解法一、使用StringBuffer

public class Main {    public static void main(String[] args) {        String str = "aarrvvh";        System.out.println(compressBetter(str));    }    public static String compressBetter(String str) {        // 检查压缩后的字符是否会变得更长        // 如果变得更长就不需要做压缩操作了，此处单列了出来        int size = countCompression(str);        if (size > str.length()) {            return str;        }        StringBuilder mystr = new StringBuilder();        char last = str.charAt(0);        int count = 1;        for (int i = 1; i < str.length(); i++) {            if (str.charAt(i) == last) {                count++;            } else {                mystr.append(last);                mystr.append(count);                last = str.charAt(i);                count = 1;            }        }        mystr.append(last);        mystr.append(count);        return mystr.toString();    }    public static int countCompression(String str) {        if (str == null | str.isEmpty())            return 0;        char last = str.charAt(0);        int size = 0;        int count = 1;        for (int i = 1; i < str.length(); i++) {            if (str.charAt(i) == last) {                count++;            } else {                last = str.charAt(i);                size += 1 + String.valueOf(count).length();                count = 1;            }        }        size += 1 + String.valueOf(count).length();        return size;    }}

采用StringBuffer时间复杂度是n，使用String则是n^2

解法二、如果不能使用StringBuffer

    public static String compressAlternate(String str){        int size = countCompression(str);        if(size >= str.length()){            return str;        }        char[] array = new char[size];        int index = 0;        char last = str.charAt(0);        int count = 1;        for(int i = 1; i < str.length(); i++){            if(str.charAt(i) == last)                count++;            else{                index = setChar(array, last,index,count);                last = str.charAt(i);                count = 1;            }        }         index = setChar(array,last,index,count);        return String.valueOf(array);    }    static int setChar(char[] array, char c, int index, int count){        array[index] = c;        index++;        char[] cnt = String.valueOf(count).toCharArray();        for(char x : cnt){            array[index] = x;            index++;        }        return index;    }

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